U.S. Pat. No. 5,282,456 (equivalent to Canadian Patent No. 2,077,126) describes a high efficiency induced draft condensing furnace with a horizontal plastic vent termination assembly. The termination vent assembly comprises a coaxial arrangement of a combustion gas vent pipe means for ejecting combustion gas discharged from the furnace and a combustion air inlet pipe means for drawing air in to assist with combustion. The combustion air inlet pipe means is concentrically disposed outwardly around the combustion gas vent pipe means. The discharge end of the combustion gas vent pipe means extends beyond the end of the combustion air inlet pipe means. It provides no means for baffling combustion gas or inlet air and does not take into account the effects of wind on the termination assembly.
Such coaxial arrangements of vent pipes and air inlet pipes are well-known in the trade.